1. Field of the Invention
The present invention relates to an apparatus for securing implanted medical devices and more particularly to an apparatus for securing implanted medical devices such as electrical stimulation leads or catheters, or a combination thereof, within a cranial burr hole and for varying the functional location of the leads or catheters within the burr hole.
2. Description of the Related Art
Medical procedures involving access to the brain through a burr hole in the skull are under increasing use. Two such procedures are electrical stimulation of the brain for such purposes as relief of chronic pain and treatment of movement disorders, and the use of parenchymal catheters for infusing pharmaceutical agents. A typical electrical brain stimulation system comprises generally a pulse generator operatively connected to the brain by a lead having at its distal end at least one electrode designed to be implanted within the brain, and having at its proximal end a connector assembly designed to connect to the pulse generator. Use of a parenchymal catheter generally involves the insertion of a catheter within the brain to dispense pharmaceutical agents at a specific targeted location.
An important aspect of these procedures, and of any other such procedures that involve instrument access to the brain through a burr hole, is the precision with which any such inserted stimulation devices are placed. As can be appreciated, the functional location of the inserted stimulation device is of critical importance and once an inserted device is properly positioned, it is equally important that the device not be moved. Even one millimeter of travel of a properly positioned stimulation device may cause unsatisfactory results or, in some cases, severe injury to the brain. Accordingly, reliable methods and apparatus for locating and fixing the positioned stimulation device in the cranium burr hole are necessary.
Previous designs of systems for securing a positioned device within a burr hole have a number of drawbacks. U.S. Pat. No. 4,328,813 issued to Ray, incorporated herein by reference, discloses a burr hole ring and cap arrangement in which the cap is positioned so as to trap a positioned electrical stimulation lead between the ring and cap by friction. That arrangement involves securing the lead off center from the burr hole in a manner such that during installation of the anchoring cap the lead is secured in place. The lead, however, often needs to be manually supported in place while the anchoring cap is being installed. The lead is thus susceptible to inadvertent movement by the physician during the cap installation period. Further, during the interaction of the cap and ring, the lip of the cap tends to pull on the lead dislodging the lead from the targeted stimulation area.
Other current burr hole rings and caps force the lead body to the center of the burr hole ring and, due to the design, to the center of the burr hole itself. Problems occur if the burr hole is not centered on the desired projection path of the lead. The burr hole ring will force the lead body to the center of the burr hole ring, which is offset from the desired lead projection path, thereby placing a load on the lead body tip, which is implanted at the targeted stimulation area in the brain. The load on the lead body tip may force the electrodes away from the targeted stimulation area or it may place an undesirable amount of pressure on the brain. The present invention is directed to overcoming the disadvantages of the foregoing systems.